1. Field of the Invention
The present invention relates to a proximity measuring apparatus, and more particularly but not exclusively to an apparatus for incorporation into road vehicles for measuring their mutual proximity.
2. Discussion of Prior Art
Proximity measuring apparatus are well known. They are incorporated, for example, into vehicles for providing information regarding their positions relative to one another.
One example of a proximity measuring apparatus is a road vehicle Doppler radar system. In use, the system is mounted onto a road vehicle and emits interrogating radiation towards other road vehicles which reflect the radiation as echo radiation back to the system for analysis therein to determine collision risk of the other vehicles to the system. A proximity measuring apparatus implemented as a microwave Doppler radar anticollision system is described in a United Kingdom patent application GB 96 02250.4.
A number of problems are encountered with the system described in the patent application GB 96 02250.4, namely:
(i) information available within other vehicles reflecting the interrogating radiation emitted from the system is not communicated back to the system; such information is potentially of benefit for more accurately determining whether or not the other vehicles represent a genuine collision hazard to the system, for example a vehicle in front is decelerating or its engine has stalled;
(ii) when a plurality of vehicles each incorporate the system, there is a risk of interference between several the vehicles when operating simultaneously within range of one another; and
(iii) spurious multipath reflections from roadside stationary objects give rise to complex and potentially misleading echo radiation to the system.
The system described in GB 96 022509 attempts to alleviate the problem in (ii) above by making frequency of emitted radiation dependent upon orientation of the system, the orientation being determined relative to the earth""s magnetic poles using a mechanical or electronic compass. However, this is potentially unreliable, especially when there are numerous vehicles each incorporating and using the system within range of one another. For example, a problem arises when a series of vehicles each incorporating the system travel in convoy in an identical direction; because the systems installed in the vehicles are orientated in an identical bearing, their systems operate at identical frequencies such that mutual interaction of the systems can occur giving rise to a risk of erroneous proximity measurement. Moreover, on account of the number of vehicles presently in use in the world, it is not feasible to allocate a unique radiation frequency band for each vehicle; problems of interference and interaction between systems in the prior art cannot therefore be ameliorated.
It is well known that radiation emitted from a source can be modulated with a signature code corresponding to the source; this allows the source to be identified when the radiation is subsequently received by demodulating it to extract its signature code. Such radiation modulation is frequently employed in radar and communication systems, for example in mobile telephones where each telephone is identified by a corresponding unique apparatus number.
A problem arises in a scenario where;
(i) there are numerous mobile sources of radiation within radiation receiving range of one another; and
(ii) the sources are constrained to operate at identical frequencies on account of limited available allocated electromagnetic radiation spectrum.
In the scenario, each source must have associated with it a corresponding unique signature code for it to be uniquely identifiable. When there are several million sources, relatively longer signature codes are required for distinguishing the numerous sources from one another. There arises then a further problem that transmission time to transmit the relatively longer codes affects rapidity with which sources can communicate information to one another; this is particularly relevant when signature code transmission occupies a relatively larger proportion of total radiation transmission time.
When the scenario relates to proximity measurement apparatus installed into road vehicles, each road vehicle requires a unique corresponding signature code for its apparatus because any combination of road vehicles in close mutual proximity can potentially occur in practice. There are presently many million road vehicles in use on roads in the world, hence many million unique signature codes are required to reduce a risk of potential confusion between signature codes and associated collision risk.
Multipath reflection from stationary objects in a road environment gives rise to a further problem when proximity measurement apparatus are used. Such multipath reflection can result in corruption of transmitted signature codes resulting in erroneous detection of a potentially dangerous collision event. It is therefore necessary for such systems to employ signature codes which are robust to corruption from multipath reflection and other sources of interfering radiation.
Signature codes are conventionally made- more robust by incorporating error correction data within them, for example parity bits, or by making the codes relatively longer by incorporating redundancy into the code. This results in a problem that their transmission duration is increased which limits code transmission repetition rate; this results in less frequent updating of proximity measurement for use in collision risk assessment, thereby increasing risk of collision.
There are therefore conflicting constraints of providing a large number of unique signature codes which each have a relatively short length and yet are robust to corruption arising from, for example, multipath interference. This represents a problem which the invention seeks to address.
It is an object of the invention to provide a proximity detecting apparatus which alleviates at least one of the problems mentioned above and provides, for example,. more reliable collision warning.
According to the present invention, a proximity measuring apparatus is provided incorporating:
(a) transponding means for receiving interrogating radiation and emitting return radiation in response thereto; and
(b) interrogating means for generating and emitting the interrogating radiation and for receiving the return radiation for determining proximity of the interrogating means relative to the transponding means, characterised in that
(c) the interrogating means is adapted to encode the interrogating radiation with a signature code comprising a plurality of concatenated data sequences;
(d) the transponding means is adapted to receive the interrogating radiation, and to encode the return radiation with the signature code, thereby enabling the interrogating means to associate the interrogating radiation with the return radiation.
The invention provides the advantage that the signature code is relatively short and that a relatively large number of unique signature code combinations with desirable correlation characteristics is possible.
The transponding means of a first vehicle may discriminate between its interrogating radiation and return radiation emitted in response thereto from interrogating radiation and corresponding return radiation of other vehicles incorporating the apparatus on the basis of signature code used. This advantage arises because each apparatus employs a signature code in its interrogating radiation and its corresponding return radiation which is unique to itself.
The apparatus is mountable, for example, into road vehicles, one apparatus for each vehicle. This enables the apparatus in a first vehicle to identify when it is likely to collide with other vehicles and provide warning to a driver of the first vehicle that corrective action is needed to avoid a collision.
For explaining the invention, a pseudo-random sequence of data bits is defined as a sequence of data bits whose values vary in a random pattern but which eventually repeats itself. A truly random sequence of data bits is defined as a sequence of data bits whose values vary in a random pattern which never repeats itself. A maximum length pseudo-random sequence of data is defined as a maximum length of a pseudo-random sequence that can be formed before the sequence is repeated.
The concatenated data sequences may incorporate concatenated pseudo-random data sequences. This provides a robust signature code which is relatively insensitive to corruption arising from Doppler frequency shift resulting from movement of the apparatus relative to one another. Pseudo-random codes also exhibit useful correlation properties.
The concatenated data sequences may incorporate concatenated Gold code data sequences. This provides an advantage of providing more unique signature codes compared to signature codes of comparable length incorporating concatenated pseudo-random sequences.
The interrogating means may incorporate correlating means for correlating the signature code encoded into the interrogating radiation with a signature code encoded into the return radiation received thereat, thereby enabling it to associate the interrogating radiation with its corresponding return radiation. This provides an advantage that the interrogating means is capable of recognising thereby return radiation emitted in response to receipt of its interrogating radiation.
The transponding means may be adapted to emit the return radiation at a frequency which is substantially different to that of the interrogating radiation received thereat, thereby enabling the interrogating means to discriminate between passive reflections of the interrogating radiation and the return radiation. This enables the interrogating means to discriminate between spurious multipath reflections, for example reflections of the interrogating radiation from lamp posts and roadside buildings, and the return radiation from a transponder.
The transponding means may be arranged to emit the return signal as the return radiation after a time delay period from receipt of the interrogating radiation, said time delay period being greater than a time required for the interrogating radiation to propagate from the interrogating means to be passively reflected and re-received thereat at greater than a threshold intensity, and the interrogating means may be adapted to discriminate between reception of delayed and un-delayed return radiation. This provides the advantage that the interrogating means is responsive only to other vehicles incorporating the transponding means and is not confused by spurious multipath passive reflections of said interrogating radiation.
The interrogating means may incorporate:
(i) an antenna for emitting the interrogating radiation and receiving the return radiation, said antenna having a directional gain response comprising a direction of enhanced gain relative thereto;
(ii) scanning means for angularly scanning said antenna; and
(iii) computing means for controlling the scanning means and determining direction of the transponding means relative to the interrogating means from scan direction of said antenna in which the return radiation is received.
Moreover, the interrogating means may incorporate computing means for determining a distance of the transponding means relative thereto, said computing means adapted to record an interval of time between emission of the interrogating radiation from said interrogating means and receipt of corresponding return radiation thereat, said computing means adapted to calculate said distance using said interval of time. This provides the advantage that the computing means is thereby capable of tracking trajectory of transponding means providing the return radiation relative to the interrogating means.
The apparatus may incorporate warning means in communication with the computing means, said computing means adapted to monitor position of the transponding means relative thereto, and to activate said warning means to provide a warning alarm when there is a risk of collision of said transponding means with said interrogating means. This provides an advantage of a user of the apparatus to take corrective action in response to the warning alarm to avoid impact or collision.
The computing means may be adapted to monitor position of the transponding means relative to the interrogating means and activate braking means to modify a trajectory of said interrogating means for collision avoidance when there is a risk of collision of said transponding means with said interrogating means.
The interrogating means may be adapted to vary its time interval duration between successive emissions of interrogating radiation therefrom. This provides an advantage of reducing the risk of two interrogating means simultaneously repetitively attempting to interrogate transponding means and thereby failing to detect its presence. This provides the advantage that if synchronous interrogation of the transponding means occurs, subsequent interrogation is likely to be dephased.
The interrogating means may be arranged to vary the time intervals in multiples of a time step, said multiples altering pseudo-randomly. This provides the advantage that two or more interrogator means simultaneously emitting interrogating radiation are likely to become more rapidly dephased.
The transponding means may incorporate sensing means for sensing at least one of acceleration, speed and orientation of said transponding means, for providing data thereto, and the transponding means may be adapted to encode said data onto the return radiation. This provides the advantage that the data is available to the interrogating means receiving the return radiation for determining with more certainty mutual collision risk.
The interrogating means may be mounted in a frontal region of a vehicle and the transponding means may be mounted in a rear region thereof. This provides a practical arrangement for the apparatus because a frontal collision of the vehicle onto a rear region of another vehicle is a most probable type of collision in practice.
For elongate vehicles, side collisions may occur. The apparatus may be incorporated into the elongate vehicle, the interrogating means in a frontal region of the vehicle and said transponding means in a rear region and side regions thereof. Incorporation of the transponding means in the side regions of the elongate vehicle provides an advantage of reduced risk of collision, especially side impact collision.
In another aspect, the invention provides a method of measuring proximity in a proximity measuring apparatus, the apparatus including an interrogator and a transponder, the method comprising the steps of:
(a) generating and emitting interrogating radiation from the interrogator, said radiation incorporating a signature code comprising a plurality of concatenated data sequences;
(b) receiving the interrogating radiation at the transponder and generating a receive signal in response thereto;
(c) storing the receive signal;
(d) generating a return signal in response to the receive signal, said return signal encoded with the signature code;
(e) emitting the return signal after a time delay period from receipt of the interrogating radiation;
(f) receiving the return radiation at the interrogator;
(g) correlating the signature code encoded into the interrogating radiation with the signature code encoded into the return radiation for associating the return radiation with the interrogating radiation; and
(h) calculating at the interrogator proximity of the transponder relative thereto from propagation direction of the return radiation relative to the interrogator and time interval between emission of the interrogating radiation and receipt of the return radiation.
In the method, the concatenated data sequences may incorporate concatenated pseudo-random data sequences. Alternatively, the concatenated data sequences incorporate concatenated Gold code data sequences.